1. Field of the Invention
This invention generally relates to the art of analyzing fluids and specifically to photoacoustic devices and methods for quantitative analysis of fluids, normally in a gaseous state.
2. Prior Art
Various analytic devices and methods using photoacoustic techniques are known in the art, e.g. as disclosed in U.S. Pat. Nos. 3,820,901, 3,938,365, 3,948,345, 4,163,382, 4,818,882, EP-A-0 231 639, EP-A-0 433 385 all of which are incorporated herein by way of reference for all purposes.
The principle that is common to photoacoustic devices and methods is interaction of light, generally in the infrared portion of the electromagnetic spectrum, with a gaseous sample containing a known analytic species of interest--which may but need not be an impurity--in an unknown concentration for generating a sonic signal dependent upon the concentration of the species of interest.
Research by applicant leading to the present invention has indicated that a major problem with many types of prior art photoacoustic devices is poor reproducibility of results, notably if unstable substances, such as ozone (O.sub.3), are the species of interest.